The present invention relates generally to waveguide assemblies and more particularly, to a method for assembling a waveguide to maintain electrical conductivity between portions of the waveguide.
Currently several very small aperture antenna ground based terminals (VSAT), referred to as remote ground based terminals, contain waveguide antenna feeds which permit remote terminals to simultaneously transmit data to and receive data from a satellite with a single directional antenna. The waveguide antenna feed system can be referred to as a Transmit Receive Isolation Assembly (TRIA). A TRIA is an integral self-contained multiple waveguide assembly for coupling a receiver and a transmitter into a single VSAT antenna. VSATs using TRIAs have increased transmission capabilities, reduced part quantity, and reduced costs to assemble and operate over VSATs not using TRIAs.
Due to the intricacies of the TRIA waveguide dimensions a xe2x80x9csplit blockxe2x80x9d or xe2x80x9cclam shellxe2x80x9d manufacturing approach is required in which two halves are used to form the waveguide. The TRIA is comprised of three waveguide microwave circuit sections. The first waveguide section is the circular waveguide section. The second section is the transmitter waveguide section. The third section is the receiver waveguide section. In order for the waveguide sections within the TRIA to receive or transmit appropriately the mating surfaces between a first half and a second half of the TRIA, in the two above approaches, need to be flat and provide a good electrically conductive seal.
Three different methods are commonly used to achieve the electrically conductive seal: soldering the waveguide halves together, brazing the waveguide halves together, and/or lapping or machining the mating surfaces and mechanically fastening the waveguide halves together.
Soldering involves applying solder flux to the first half of the waveguide and applying solder paste to the second half of the waveguide. A mating surface of the first half is then assembled to a mating surface of the second half to form the waveguide. After assembling the first half to the second half to form the waveguide, the waveguide is baked to re-flow solder and create a metal-to-metal bond between the first half and the second half. The waveguide is then cleaned to remove solder flux. The disadvantages to soldering are that soldering is labor intensive and therefore costly. The solder may potentially drip/flow into the waveguide causing the waveguide to fail electrical performance. Furthermore, if the waveguide is not cleaned completely, the solder flux can cause metal corrosion.
Brazing involves applying solder flux to areas where a solder bond is needed. The first half of the waveguide is then assembled to the second half of the waveguide. The waveguide is dipped in a molten metal bath to braze the mating surface of the first half to the mating surface of the second half. Brazing is also labor intensive and therefore costly. In aluminum brazing, the temperature of the molten metal bath is close to the melting point for the waveguide aluminum base metal. Often this causes the waveguide to warp or distort when it is placed in the molten metal bath.
Lapping or machining involves lapping or machining the mating surfaces of each waveguide half to provide a flat mating surface for electrical conductivity and assembling the two waveguide halves with an adequate number of mechanical fasteners. The drawbacks to lapping or machining are that variations to the internal waveguide dimensions are introduced which can cause decreased electrical performance, thereby not meeting electrical requirements such as frequency response, power loss, or rejection requirements. Also because of variation in the mating surfaces the waveguide may require electrical tuning after or during the assembly process. A very flat mating surface prior to machining or lapping each waveguide half is a requirement to minimize lapping variances. If a half is slightly bent coming off the mold, lapping or machining the bend flat can cause significant waveguide dimensional changes and therefore degrade the electrical performance of the waveguide. Lapping and machining are also sensitive to operator performance. Further, if an environmental moisture seal is required for a particular application additional sealing process steps are needed in lapping and machining.
It would therefore be desirable to provide a method of assembling a waveguide that reduces costs, reduces defects, increases performance, increases production quantity for a specified time frame, minimizes steps involved, and removes operator error.
One object of the invention is to reduce the number of defectively manufactured parts in the assembly method of a Transmit Receive Isolation Assembly (TRIA) contained within a ground based terminal. Another object of the invention is to manufacture a TRIA with less costs and increased performance and production volume.
In one aspect of the present invention a method is provided for assembling a waveguide. The method of assembling a waveguide comprises the steps of: applying a gasket to the mating surface of a first half of the waveguide, fastening the first half to a second half of the waveguide, and disposing the gasket between the mating surface of the first half and a mating surface of the second half.
In a further aspect of the present invention a waveguide is also provided having a first half and a second half. The mating surface of the first half is aligned with the mating surface of the second half. A gasket is disposed between the mating surface of the first half and the mating surface of the second half. The first half is fastened to the second half with a gasket therebetween. The gasket may take the form of a conductive epoxy or a malleable metal pre-form.
One advantage of the present invention, is that there is minimal tolerance variance in waveguide mating surfaces since no lapping or machining occurs to the waveguide halves prior to assembly, therefore no electrical tuning is needed. Another advantage of the invention is that both electrical conductivity and environment moisture seal are obtained with a single automated assembling method. Furthermore, an automated stencil or screen machine can be used to apply a low tolerance, highly repeatable layer of conductive epoxy which creates a bond between the first half and the second half with optimized electrical conductivity. The created bond eliminates the need for strict tolerances on overall flatness on the waveguide first mating surface and the second mating surface, thereby increasing efficiency of production and reducing the number of nonconforming parts. The epoxy also allows the waveguide to be electrically tested before curing, thereby allowing the waveguide assembly to be repaired if the waveguide fails electrical testing. The stencil or screen can also be designed to optimize an environmental moisture seal created by the epoxy that in turn increases the moisture seal production yield (quantity of properly sealed waveguides per time).
Another advantage of this invention is that no hand sealing of the screws, flange faces, or seams is needed which in turn reduces labor costs and improves production yields for moisture sealing. The assembly method is also less sensitive to operator performance over traditional methods. The aforementioned allows for high production quantities.
Therefore, large volume, low cost waveguide assembly is possible due to the stated method advantages. The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.